1. Technical Field of the Invention
This invention relates to integrated circuit devices. More particularly, this invention relates to improved topside sealing of integrated circuit devices.
2. Background Art
In the production of integrated circuit devices, the topside metallized layer must be hermetically sealed to prevent attack by moisture or other corrosive environmental effects. Conventionally, an oxide layer is first deposited over the metal layer, masked to open areas, and then a nitride sealing layer, such as silicon nitride, is deposited in a thickness of about 8000 Angstroms followed by a second masking operation to open up areas in the nitride layer.
This double deposition, with intervening masking steps, is costly and can also result in disruption of the integrity of the nitride seal adjacent to the openings if the nitride layer is not sufficiently thick. On the other hand, the thicker the nitride layer, the more brittle the nitride layer becomes which can, in turn, result in cracking which will also disrupt the seal. As shown in FIG. 1, which represents the prior art, if the nitride layer, in the immediate vicinity of the opening in the areas shown within the dotted lines denoted by the numeral 10 in FIG. 1, cracks or in any other way fails, moisture can penetrate along the metal-oxide interface to completely destroy the seal. Furthermore, as previously stated, this type of sealing process results in the need for two independent depositions with two separate maskings to provide the necessary contact openings to the metallized layer being sealed.
The two mask process is needed to obtain the overlap of the nitride layer inside the opening in the oxide layer over the metal pad as shown in FIG. 1. Usually the second mask is an undersized version of the first mask used for etching. The first mask and etch open up the oxide over the metal whilst the second mask and etch open up the nitride over the metal.
It would, therefore, be desirable to provide an improved seal which would, at the same time, eliminate some of the intermediate processing steps.